Note: Descriptions are shown in the official language in which they were submitted.
V ~ ~ _01--11.~ 1
~7~43Z
The present invention is directed to improvements
in carburetors and more particularly to improvements in the
construction of carburetors wherein separa~ely formed component
members are combined to provide a carburetor assembly.
Carburetors are known to include complex systems
of passages which are difficult to cast and drill, and to
include numerous components which are difficult to assemble
such as throttle plates, inlet valves, needle valves, orifice
members and the like. Efforts have been made to simplify
the manufacture of carburetors by means of subassemblies,
however, some of the difficultîes still remain particularly
with respect to the drilling of intersecting passages, and
the assembly of components such as throttle plates, needle
valves, inlet valves and the like.
The present invention relates to improvements in
carburetors constructed from assembled components wherein
the several components are formed for ease of engagement
with adjacent components 9 at least some of the components
including simple pa~terns of recesses and apertures which in
combination with adjacent components provide a desired
system of passages.
The various components may be formed so as to
virtually eliminate machine surface finishing, and may be
formed of various materials such as metal, or synthetic
resins.
The patterns of apertures and recesses in the
component members are susceptible to arrangement in a
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manner to provide auxiliary functions in combination with
the system of fuel passages such as a metering chamber,
fuel pump and accelerator pump.
The components are formed for ease of assembly ~ ,
with each other, certain of the components being nestible
with respect to each other and certain components providing
interlocking means whereby adjacent components are located
in a desired relationship. -
Further, interchangeable components may be used in
the assembly where modifications of fuel or air passages or
auxiliaries are desirable for use with particular engines.
Broadly speaking, therefore, the present invention
provides a carburetor construction comprising: a base plate
having a substantially planar surface including an opening
adapted for connection to an air inlet passage of an
internal combustion engine, the opening defining a socket
and the planar surface including a groove extending
transversely with respect to the socket; a throat member
defining a fuel-air mixing passage mounted on the base
plate having a mixture outlet portion thereof in alignment
- with the opening in the base plate, the throat member having
an air inlet portion spaced from the mixture outlet portion
and including fuel aperture means extending through a wall
` portion thereof between the air inlet portion and the
mixture outlet portion, the throat member being received
within the socket and including a pair of oppositely disposed
slots aligned with the groove; a rotatable throttle shaft
extending through the slots and journalled in the groove,
the throttle shaft including a throttle plate disposed in
.,,,
the mi~ture outlet portion of the throat member providing a
variable restriction in the mixing passage; and a fuel module
.
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mounted on the base plate receiving the throat member
including fuel channel means arranged and disposed for
communication with a source of fuel and with the aperture
means in the throat member, the base plate, throat member
and fuel module being secured in interlocking engagement.
DRAWINGS
FIGURE 1 is an exploded view of components of a
carburetor construction according to the present invention;
FIGURE 2 is a top view of a carburetor assembled
: 10 for components shown in FIGURE l;
FIGURE 3 is a side view of the carburetor shown in
FIGURE 2;
FIGURE 4 is a bottom view of the carburetor shown
in FIGURE 2;
FIGURE 5 is a schematic view of the carburetor :
illustrating operation at idle condition; ;
FIGURE 6 is a sch~matic view similar to FIGURE 5
illustrating operation at open throttle condition;
. FIGURE 7 is a fragmentary section view showing
;~ 20 detail of throttle adjusting means to enlarged scale, taken
along the line 7-7 of FIGURE 2; ^
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FIGURE 8 is a fragmentary section view showing
detail of accelerator pump means to enlarged scale, taken
along the line 8-8 of FIGURE 2;
FIGURES 9, 10, ll are top, side and bottom views
respectively of a typical rotatable fuel adjusting plug
shown to enlarged scale;
FIGURES 12, 13 are top and side views of a portion
of the accelerator pump means shown to enlarged scale;
FIGURE 14 is a top view of a throat member defining
a fuel-air mixing passage shown to enlarged scale;
FIGURE 15 is a section view of the throat member
taken along the line 15-15 of FIGURE 14;
FIGURE 16 is a section view similar to FIGURE 15
of an alternate embodiment of throat member;
FIGURE 17 is a perspective view of a throttle
: member shown to enlarged scale;
FIGURE 18 is a view of the upper surface of the
base plate shown to enlarged scale;
FIGURE l9 is a plan view of a gasket;
FIGURES 20, 21 are plan and side views respectively
of a lower diaphragm;
FIGU~E 22 is a plan view to enlarged scale of the
lower surface of a metering plate forming a portion of a
fuel module;
FIGURE 23 is a plan view to enlarged scale of ~he
upper surface of the metering plate shown in FIGURE 22;
FIGURE 24 is a plan view to enlarged scale of an
upper diaphragm;
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075181-~ST
6432
FIGURE 25, is a plan view to enlarged scale of ~he
lower surface of a cover plate forming a portion of a fuel
module;
FIGURE 26 i5 a fragmentary section view to enlarged
scale showing an alternate embodiment of fuel adjusting
plug;
FIGURE 27 is a plan view to enlarged scale of the
lower surface of a cover plate for the embodiment of FIGURE
26;
FIGURE 28 is a perspective view to enlarged scale
of an alternate embodiment of carburetor construction;
FIGURES ~9, 30, 31, 32 are fragmentary views to
enlarged scale showing detail of a modified form of carburetor;
and
- FIGURES 33, 34, 35 are section, top and side views
~; respectively, to enlarged scale, showing a further alternate
embodiment of a throat member.
Referring initially to FIGURES 1-4 there is shown
an improved carburetor construction 50, the components
thereof being sho~n in disassembled relationship in FIGURE
1. In somewhat more detail, the carburetor includes a base
~ plate 51, a fuel module 52 including a metering plate 53 and
7; a cover plate 54, a throat member 55 defining a mixing
~: passage and a throttle member 56. Base plate 51, metering ~:~
plate 53 and cover plate 54 include grooves, recesses, ~ :
channels and openings, to be described in more detail
hereinafter, which nestibly receive other components o~ the
carburetor and serve to retein the various components in
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075181-MST 1~7 ~3~
desired relationship to each o~her. In addition to the
above named components, FIG~RE 1 shows a gasket 57, throttle
return spring 58, lower diaphragm 5g, fuel inlet valve 60,
valve lever 61, valve spring 62, throttle adjusting screw
63, accelerator pump shoe 64, ball check 65, air bleed
insert 66, upper diaphragm 67, accelerator pump return
spring 68, high speed adjusting plug 69, idle adjusting plug
70, resilient collars 71, 72 for respective adjusting plugs,
a sight glass 73, and retaining screws 74, 75, 76, 77.
Referring now to FIGURES 5 and 6, the nested
relation of components is shown to enlarged scale in vertical
dimension while ~he longitudinal dimension has been distorted
in an effort to show the path of the fuel channels in planar
view, certain of the components being displaced for the sake
of clarity in illustrating their functional interaction with
adjacent components. The recesses and cavities shown schematically
in FIGURES 5 and 6 are shown in true relationship in detailed
views of the base plate, metering plate and cover plate
found in FlGURES 18 through 25, to which reference may be
had.
Referring now to FIGURES 1, 4, 5 and 18, the base
plate 51 will be described in more detail. Base plate 51
includes a lower surface 81 adapted for mounting on a flange
surrounding the air inlet of an internal combustion engine.
The upper surace of base plate 51 includes a substantially
planar sur~ace portion 82 interrupted by upsta~ding mounting
bosses 83, 84, locating pins 85, 86, and by various grooves,
rPcesses and openings described below. Mounting bosses 83,
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075181-MST
~76~3Z
84 include mounting holes 78, 79 to receive screws for
securing the carburetor to an engine.
Base plate 51 includes a major opening 87 having a
shoulder portion 88 and a beveled portion 89 defining a
socket for receiving throat member 55. ~eveled key slots 90, 91
are formed in the opening for positioning throat member 55
with respe.ct to base plate 51. As seen in FIGURE 1, throat
member 55 is provided with a cylindrical portion 9~ for
engaging opening 87, a shoulder 93 for engaging shoulder
portion 88, a be~eled edge 94 for engaging beveled portion
89, and beveled key portions 95, 96 for engaging key slots
90 and 91. The circumferentially disposed key portions and
key slots serve to locate the throat member in a selected
relationship to the base plate, while the beveled surfaces
provide fluid tight seals which are easy to assemble.
Parti-cylindrical grooves 97, 98 are formed in
planar surface portion 82 extending so as to intercept
opening 87. The par~i-cylindrical grooves 97, 9~ provide
bearing surfaces for journal portions 99, 100 of rotatable
throttle member 56. Parti-cylindrical surface 97 is intercepted
by a small opening 101 for receiving idle air adjusting cam
102 of throttle member 56. Similarly, parti-cylindrical
surface 98 is intercepted by a second small opening 103
arranged for receiving accelerator pump cam 104 of throttle
member 56. FIGU~ES 7, 8 and 17 show the cams 102, 104
related to throttle member 56 and base plate 51.
The interlocking engagement of base plate 51 with
throat member 55 and throt~le member 56 can be seen in the
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0751~1-MST
~07~43'~
.
left hand portion of FIGURE 5. In the configuration shown
in FIGURE 5, throat member 55 is formed with a restricted
band 105, defining a venturi section, a frusto-conical
section 106 and a cylindrical section 107, between the air
~nlet end 108 and the air outlet end 109, defining a fuel
and air mixing passage. A main fuel aperture 110 penetrates
a wall portion of throat member 53 in the vicini~y of restricted
band 105, and an idle fuel aperture 111 penetrates the wall
in the cylindrical portion of the mixing passage. Additional
fuel apertures such as transitional orifice 112 may penetrate
the wall if desired. Throat member 55 includes slots 113,
114 arranged for e~bracing throttle member 56 such that
throttle plate portion 115 thereof bears a selected relation-
ship to the fuel apertures 110, 111 and 112.
Continuing now with the description of further
openings and recesses in base plate 51 reference is made to
FIGURE 5 and FIGURE 18 wherein the section line 5A-5A
generally indicates the section view shown in FIGURE 5.
Recess 116 is open to atmosphere through vent 117 and
cooperates with lower diaphragm 59 to form a bounce chamber
for reducing pulsation in the fuel channels of fuel module
52. Adjacent recess 118 opens through lower surface 81 by
means of opening 119 adapted for co~munication with a source
of pulsating pressure such as the crankcas~ of an internal
combustion engine. Recess 118 in cooperation with a portion
of diaphragm 59 provides a pulse operated fuel pump. The
next adjacent recess 120 is open to atmosphere through vent
075181-MST
1~76~32
121, and in cooperation with a portion of lower diaphragm 59
provides the dry side por~ion of a metering chamber. An
idle fuel channel 122 is recessed into planar surface 82 and
opens into beveled key slot 90 for communication with idle
fuel aperture 111 in throat member 55. Base plate 51 also
includes four threaded holes 123, 124, 125, 126 for re-
ceiving retaining screws 74, 75, 76, 77. Further, base
plate 51 includes an air bleed inlet 127 and an air bleed
outlet 128.
Referring now to FIGURE l9, the gasket 57 is shown
to a scale different from that of F~GURE 18, however, it is
believed that the openings in gasket 57 can be readily
associated with the corresponding recesses and openings in
base plate 51. For example, the four openings 135, 136,
137, 138 correspond with threaded holes 123, 124, 125, 126
permitting passage of retaining screws 74, 75, 76, 77. In a
similar fashion, circular opening 139 corresponds with
metering chamber recess 120, irregular opening 140 corres-
po~s with pump chamber recess 118, and square opening 141
correspon`ds with bounce chamber recess 116. Small openings
142, 143 receive locating pins 85 and 86. Aperture 144
corresponds with air bleed outlet 12~, and idle fuel aperture
145 overlies idle fuel channel 122. Rectangular cutout 146
corresponds with accelerator pump cam opening 103. Arcuate
edge 147 is adjacent socket opening 87 when in place on base
plate 51 and may, if desired, include one or more notches
148, 149 which can be arranged in a coded pattern. Where
multi-purpose and or interchangeable throat members are
available, a coded notch pattern on gasket 51 can be employed
,
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U75181-M~T
1~643Z
for the purpose of checking the identification and orient-
ation of a ~hroat member.
Lower diaphragm 59 forms a resilient membrane
between base plate 51 and fuel module 52, and is shown in
FIGURES 20 and 21 to a scale similar to that of gasket 57 in
FIGURE 19. Diaphragm 59 is formed preferably of a flexible
resilient rubber-like material of a composition resistant to
deterioration in the presence of petroleum products. Lower
diaphragm 59 includes four openings 155, 156, 157, 158 to
permit passage of retaining screws 74, 75, 76 and 77. Small
openings 159, 160 are arranged to receive locating pins 85,
~6. Air bleed aperture 161 is arranged to communicate with
air bleed outlet 128 when in place on base plate 51. Idle
fuel aperture 162 i9 arranged for communication with idle
fuel channel 122 when in place. A depression 163 is formed
in lower diaphragm 59 arranged for nesting in metering
chamber recess 120 of base plate 51. A rectangular cutout
164 corresponds with accelerator pump cam opening 103 and
arcuate edge 165 is formed to lie adjacent socket opening
87. A pattern of coded notches such as 166, 167 may be
included if desired as in the case of the gasket 57.
Referring now to fuel module 52, metering plate 53
is shown in bottom plan view in FIGURE 22 and in top plan
view in FIGURE 23, the schematic section view of FIGURE 5
being taken substantially along the section lines 5B-5B.
The openings and recesses in metering plate 53 which are
congruent wi~h cooperating openings and recesses in base
plate 51 are shown in more detail in FIGURE 22.
A large opening 175 is included in metering plate
53 arranged for embracing a throat member 55. Opening 175
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0751~1 MST
1~7 ~3~
includes a tapered surface 176 arranged for engaging portions
of a throat member to form a fluid tight seal adjacent the
fue]. apertures therein. A coded pattern of notches such as
177, 178, 179, 180 may be formed adjacent opening 175 for
the purpose of correlating a metering plate with a selected
one of interchangeable throat members. Lower surface 181 o~
me~ering plate 53 includes a pair of parti-cylindrical
grooves 182, 183 providing bearing surface for journal
portions 100, 99 of throttle member 56. An accelerator pump
cam opening 184 intercepts bearing surface 182, while a
threaded opening 185 and recess 186 are formed adjacent
bearing surface 183 to receive throttle adjusting screw 63.
Four through holes 187, 188, 189, l90 are provided to permit
passage of retaining screws 74, 75, 76 and 77 through the
metering plate. A pair of small recesses 191, 192 are
arranged to receive locating pins 85 and 86 of base plate
51. An air bleed aperture 193 is arranged for communication
with air bleed outlet 128 of base plate 51-.
Metering plate 53 is provided with a ~uel inlet
tube connector 200 communicating wi~h a fuel cavity 201. An
opening 202 extends from fuel cavity 201 through top surface
203 of metering plate 53 defining a valve seat. Fuel cavity
201 is arranged to overlie bounce chamber recess 116 of base
plate 51.
A fuel pump recess 204 is formed ad~acent fuel
cavity 201 arranged to overlie fuel pump recess 118 in base
plate 51. ~uel pump recess 204 includes an inlet opening
-11-
0751~ lST
1~76~3;;~
205 and an outlet opening 206 defining a valve seat.
A wet side metering chamber recess 207 is formed
in lower surface 181 of metering plate 53 arranged to over-
lie dry side metering cham~er recess 120 of base plate 51.
An inlet valve seat 208 is formed in a raised boss 209 pro-
jecting from top surface 203, the valve seat 208 being
arranged for cooperation with fuel inlet valve 60. Metering
chamber recess 207 includes further recessPd portions 210,
211, 212 providing mounting surface for valve lever 61 and
valve spring 62. A small socket 194 is recessed into top
surface 203 concentric with air bleed aperture 193 arranged
to receive cup-like air bleed insert 66.
An idle fuel metering orifice 213 is in communication
with metering chamber recess 207 and penetrates top surface
203 of metering plate 53. A hi~h speed or main fuel metering
orifice 214 is spaced from idle orifice 213 and also communicates
with metering chamber recess 207 and penetrates top surface
203 as shown in FIGURES 22 and Z3, metering orifices 213,
214 are shown as circular apertures, however, other shapes
of apertures may be employed. For example, one desirable
aperture configuration is in the form of a triangle having
converging edges. The aperture configuration of a metering
orifice is selected in combination with the metering surface
of an associated adjusting plug 69 or 70 so as to provide a
desired variation in flow area in response to rotation of
the adjusting plug.
Referring to FIGURE 23 a recess 215 is formed in
top surface 203 adjacent idle fuel orifice 213. Recess 215
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U75181-M~T
1~76~3'~
is of a shape which defines three radial e~tension portions
~16, 217, 218 of top surface 203 upon which the metering
surface of adjusting plug 7û rests. Extension 216 provides
a metering surface surrounding ori~ice 213. A well 219 is
formed adjacent radial extension portion 216 arranged for
receiving a projecting portion of adjusting plug 70. The
opening of well 219 with respect to idle orifice 213 is
selected with reference to the con~iguration of metering
surface on adjusting plug 70. A preferred configuration of
metering surface is similar to the surface defined by ledge
305 of metering plug 69, shown in FIGURE 11, the metering
plugs 69 and 70 being substantially identical.
A similar recess 220 is formed in top surface 203
adjacent main fuel orifice 214. Recess 220 defines three
radial surface extensions 221, 222, and ~23 for supporting
high speed adjusting plug 69 and includes a well 22~ for
locating plug 69 with respect to orifice 214. Extension 221
provides a metering surface surrounding orifice 214. Recess
220 includes a fuel outlet opening 225 which communicates
with high speed fuel channel 226 in lower surface 181 of
metering plate 53. High speed fuel channel 226 in turn
communicates with opening 227 which penetrates recess 228.
A counterbored portion 229 of recess 228 provides a valve
seat for check ball 65. .
The high speed portion of the fuel channel means ~ '
including metering chamber 207, high speed orifice 214,
recess 220, opening 225, channel 226, opening 227 and recess
228 is shown schematically in FIGURE 6.
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~75181-~ST
~(~76~3Z
Referring to FIGURE ~3, top surface 203 of metering
plate 53 includes a pair of aligning pins 230, 231 projecting
therefrom. A recess 232 is formed in top surface 203
surroundlng accelerator pump opening 184 and defines a stop
surface 233 arranged for limi~ing movement of accelerator
pump shoe 6~.
An idle fuel channel opening 234 extends between
top surface 203 and lower surface 181 of metering plate 53
as shown in FIGURES 5, 22 and ~3.
Upper diaphragm 67 forms a resilient membrane
between metering plate 53 and cover plate 54, and is shown
in plan view in FIGURE 24. Diaphragm 67 is formed preferably
of a flexible resilient rubber-like material of a composition
resistant to damage from contact with petroleum based products.
Upper diaphragm 67 includes a large opening 240
corresponding with opening 175 in metering plate 53, and a
pair of smaller openings 241, 242 corresponding with recesses
215 and 220 respectively of metering plate 53. A pattern of
four holes 243, 244, 245 and 246 is arranged to permit
passage of retaining screws 74, 75, 76 and 77. A pair of
openings 247 and 248 is arranged for receiving aligning pins
230 and ?.31 projecting from metering plate 53. An air bleed
aperture 249 is located for communication with air bleed
aperture 193 in metering plate 53. An idle fuel aperture
250 is loca~ed for alignment with idle fuPl channel opening
234 in metering plate 53. A further opening 251 i9 located
for alignment with valve seat 2~9 in order to facilitate
assembly of ball check 65. The opening 252 is arranged to
overlie pump inlet opening 205 and defines a flap valve
-14-
07~181-MST
~al7~32
portion 253 arranged to overlie opening 202 in metering
plate 53. Opening 254 includes a distant portion Z55
arranged to receive raised boss 209. Opening 254 also
defines a flap valve 256 arranged to overlie pump outlet
opening 206. The broken line 257 is shown in FIGURE 24 to
indicate a portion of diaphragm 67 which is flexed with
respect to recess 232 by operation of accelerator pump shoe
64.
Cover plate 54 is described in more detail below
referring to FIGURES 5, 6 and 25. The lower surface 265 of
cover plate 54 is shown in plan view in FIGURE 25, while
various sections are shown in FIGURES 5 and 6 taken generally
along the section lines 5C-5C, 5D-5D and 6-6 and 6A-6A of
FIGURE 25. A large through opening 266 is formed in cover
plate 54 provided with a tapered wall 267 arranged for
embracing throat member 55. A pattern of four mounting
holes 268, 269, 270 and 271 is arranged to permit passage of
retaining screws 74 - 77. A pair of small recesses 272, 273
is arranged to receive aligning pins 230 and 231 of metering
plate 53. An opening 274 is formed in cover plate 54 .,
arranged to overlie well recess 224 in metering plate 53. A
shoulder 275 and cylindrical wall 276 are concentrically
disposed about opening 274 and form, in combination with
recess 220 and surface 221, a pocket for receiving high
speed adjusting plug 69. A similar opening 277 is ~ormed
adjacent opening 274 and is surrounded by a shoulder 278 and
cylindrical wall 279 defining a pocket arranged for re- :
ceiving idle adjusting plug 70, the idle pocket being
related to recess 215 and metering surface 216 of metering
plate 53. A narrow elongated recess or channel 280 extends
-15~
0751~1-MST
1076~3Z
from cyLindrical wall 279 to a point where it will overlie
idle fuel channel opening 234 in metering plate 53. Another
narrow elongated recess or channel 281 extends from cylindrical
wall 279 to a point where it will overlie air bleed aperture
193 of metering plate 53. Recess 280 extends along a portion
of section line 5C-5C of FIGURE 25 which recess 281 extends
along section line 5D-5D thereof. The recesses 280 and 281
are shown in section in FIGURE 5 in association with idle
adjusting plug 70. A third narrow recess or channel 282
extends from cylindrical wall 276 of the high speed ad-
justing pocket to a point intercepting accelerator pump
aperture 283. A stepped recess 284, 285 is shown in broken
lines in FIGURE 25 indicating that the stepped recess is
formed in the upper surface of cover plate 54 where it
serves to mount the sight glass 73. An aperture 286 communicates
the stepped recess 2~4, 285 with accelerator pump recess
287. The relationship of the accelerator pump recess 287
with the aperture 286, 283, recess 284, 285, channel 282 and
high speed pocket 276 is shown in section in FIGURE 6, being
taken substantially along the line 6A, 6A of FIGURE 25.
A recess 288 is formed in lower surface 265 of
cover plate 54 arranged to provide communication between
openings 202 and 205 of metering pla~e 53. An adjacent
recess 289 in surface 265 ls arranged to provide commu-
nication between opening 206 and inlet valve seat 208 of
metering plate 53.
Ridges such as 290-294 are formed on surface 265,
surrounding th~ recesses formed therein. The ridges, indent
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075181-MST
1~7~43Z
diaphragm 67 when the carburetor is assembled and serve to
isolate one recess from adjacent recesses.
Adjusting plugs 69 and 70 can be identical in
construction if so desired, and adjusting plug 69 is shown
to enlarged scale in FIGURES 9-11. As seen in top view in
FIG~RE 9, plug 69 has a neck portion 300 including a screw-
driver slot 301 and an arrow 302. A coliar 303 extends
concentrically about neck portion 300 and defines a shoulder
304. When plug 69 is assembled with cover plate 54, a
resilient rubber ring such as an O-ring 71 engages shoulder
304 providing a fluid tight seal and serving to bias the
plug against metering surface ~21 of metering plate 53. A
spiral ledge 305 is disposed eccentrically with respect to
collar 303 and is arranged to overlie a metering orifice
such as orifice 214 in metering surface 221. Spiral ledge
305 defines a metering surface 309 on plug 69. Three spring
fingers 306, 307, 308 are arranged in a circular pattern
concentric with collar 303 and extend from metering surface
309. Spring fingers 306, 307 and 308 are of such dimension
as to be easily inserted in a well such as 224 of metering
plate 53. When the spring fingers are inserted in the well,
spiral ledge 305 is related to a respective metering orifice ;:
such that rotation of the plug covers or unco~ers the
orifice to change the effective area thereof. Metering plug ~:
70 is essentially identical to metering plug 69 and it is ;
thought that a detailed description of plug 70 is not
required.
Accelerator pump shoe 64 is shown to enlarged
scale in FIGURES 12 and 13 where it is seen to consist of a
-17-
0751~1-MST
~)76432
cap portion 310 and a stem portion 311. Cap portion 310 is
arranged to engage upper diaphragm 67 while stem portion
311 serves to guide ~he shoe with respect to openings 103
and 184. The relationship of shoe 64 to other portions of
~he carburetor is shown to e~larged scale in ~ragmentary
section view FIGURE 8.
Referring now to FIGURES 14 and 15, a multi-
purpose throat member 55 is shown to enlarged scale in-
cluding a pair of coding keys 315, 316 and an additional
main fuel aperture 317, idle aperture 318 and transitional
aperture 319. As seen in the left hand side of FIGURE 15
main orifice 110 and transitional orifice 112 communicate
with each other through slot 320 while idle orifice 111 is
isolated therefrom. As seen in the right hand side of
FIGURE 15, idle orifice 318 communicates with transitional
orifice 319 by means of slot 321 while main aperture 317 is
isolated there~rom. A comparison of FIGURES 14, 19, 20 and
~2 will provide a better understanding of the cooperation of
coding keys 315, 316 with the coded notches 177, 178, 179,
180 for selecting which pattern of fuel orifices is rendered
effective in a multi-purpose throat member. For example, if
it is desired to render fuel apertures 317, 318, 319 effect-
i~e, code key 316 should be engaged with code notch 178 in
metering plate 53, in which case code notches 149 and 167 in
the gasket 57 and diaphragm 59 should be open while code
notches 148 and 166 should be left blank. On the o~her hand
if it is desired to assemble throat member 55 so as to
render ~uel apertures 110, 111 and 112 effective, then code
key 315 should be engaged with code notch 177 in the metering
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~75181-MST ~76432
plate in which case only the code notches 148, 166 are
formed in gasket 57 and diaphragm 59.
An al~ernate embodiment of throat member is
designated by the reference character 325 and shown in
section to enlarged scale in FIGURE 16. Throat member 325
includes a cylindrical portion 326, an inclined frusto-
conical portion 327 and a restricted band 328 defining a
venturi section which is inclined and eccentric with respect
to cylindrical portion 326. An idle fuel aperture 329 opens
through a wall of cylindrical portion 326, and a main fuel
aperture 330 opens into restricted band 328. Normally, flow
through the throat is from the air inlet end 331 through the
mixture outlet end 332, however, certain engines are known
to impose cyclic reverse flow or rebound on the carburetor
throat as a result of closure of the engine inlet valve. In
some cases the reverse flow or rebound may create zones of i
static pressure adjacent a fuel aperture which can impede
flow of fuel through the aperture into the mixing passage.
The inclined and eccentric arrangement of the restricted
band 328 and frusto-conical portion 327 permits unimpeded
flow in the forward direction from air inlet end 331 to
mixture outlet end 332, but creates turbulence if the
mixture attempts to flow in the opposite direction thereby
preventing the formation of static pressure zones which
could interfere with proper flow of fuel through the fuel
apertures into the mixing zone. The substitution of throat
member 325 in place of throat member 55 may therefore be
desirable when the carburetor is to be mount~d on an engine
known to create rebound pulses in the mixing passage.
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07Sl81-MST ~76~32
Throttle member 56 is shown in perspective to
enlarged scale in FIGURE 17. The journal portions 99, lO0,
cam portions 102 and 104 and throttle plate ll5 have been
described hereinabove and it is thought to be unnecessary to
repeat the description of the above named portions. In
addition to the above, shaft portion 335 is provided with a
slot 336 for engaging return spring 58, while shaft portion
337 is provided with a disc member 338 including openings
339. The openings 339 provide means for attaching an
operating member to the throttle member such that it can be
rotated against the bias of return spring 58.
A modi~ied form of metering plate 345, cover plate
346 and high speed adjusting plug 347 is shown in fragmentary
section in FIGURE ~6 which can be compared with FIGURE 6.
A plan view of the lower surface of the modified form of
cover plate 346 is shown in FIGURE ~7 which is comparable
with FIGURE 25. Metering plug 347 includes a neck portion
348 having a screw driver slot 349 formed therein and a
shoulder 350 surrounding neck portion 348. The lower
portion of metering plug 347 has a collar 351 which is
concentric with neck portion 348 and which is rotatable in a
recess 352 in metering plate 345. An eccentric recess 353
is formed in the lower end surface of plug 347 arranged such
that rotation of the plug is effec~ive to vary the effective
area of metering orifice 354. A vertical internal passage
355 includes a valve seat 356 arranged to receive check ball
357. A horizontal internal passage 358 provides communication
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between the check ball 357 and pocket wall ~59. A narrow
recess 360 provides colmnunication between pocket wall 359
and tlle large opening 361 which embraces a throat member
such as 55. I desired, the neck portion 348 of plug 347
can be pro~ided with an opening 362 which is normally closed
by a removable plug 363 in order to facilitate installation
and removal of check ball 357. A similar construction of
metering pocket and adjusting plug can be used for the idle
system however, a check ball is not required in the idle
system and as a result the metering plug for the idle system
can be modified to eliminate the check ball and valve seat.
Comparison of modified cover plate 346, FIGURE 27
with cover plate 5~, FIGURE ~5 reveals that the openings and
recesses are quite similar. Significant differences are
that the high speed fuel outlet channel has been relocated,
and ~hat accelerator pump, sight glass and connecting fuel `
channel have been eliminated. An accelerator pump is
desirable for some applications of the carburetor, but is
not required for all such applications and may be eliminated
when desired.
FIGURE 28 is an exploded perspective view of a
modified form of carburetor 370 which is substantially
similar to the carburetor 50 described hereinabove. One
difference between carburetor 50 and carburetor 370 is that
the base plate 371, metering plate 372 and cover plate 373
are secured together by means of a pair of spring clips 374,
375 which eliminates the need for retaining screws. Spring
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107~32
clip 374 includes opposed upper 376 and lower 377 ridge
portions arranged to engage the upper surface 37~ of cover
member 373 and a lower surface 379 of base plate 371. A
cutout 380 is provide in clip 374 to permit passage of fuel
inlet connector 381. Spring clip 375 includes opposed upper
3~2 and lower 383 ridges arranged for engagement with
surfaces 378 and 379.
A further difference between carburetor 50 and
carburetor 370 is the provision of a choke mechanism 390
which is shown in enlarged section view in FIGURES 29 and
30. Choke 390 includes a cup like air inlet member 391, a
plunger 392 and a spring 393. Member 391 includes a central
opening 394 for receiving plunger 392 and a series of
peripheral air inlet openings 395. A series of spring
fingers 396 is formed on member 391 arranged to engage with
a grooved collar 397 protruding from upper surface 378. If
desired, collar 397 can be formed as an extension of the air
inlet end of a throat member 398. The arrangement of
plunger 392 with respect to air inlet openings 395 is such
that depression of the plunger reduces the effective area of
the openings 395 thereby decreasing the flow area available
for air inducted into the throat member.
A further modification of the carburetor is shown
in FIGURES 31 and 32 where it is desired to provide optional
orientation for a fuel connector. A modified metering plate
400 includes a tapered opening 401 com~unicating with a fuel
cavity 402. An annular series of depressions 403 is disposed
about the opening 401. A fuel tube connector 404 is provided
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with a spring finger detent portion 405, 406 extending from
a conical portion 407, the conical portion being provided
with sealing beads 408, 409. The body of connector 404 is
also provided with raised portions 410 engageable with
depressions 403. A tube connector nipple 411 extends from
the body of tube connector 404. An internal passage 412
provides communica~ion between the nipple end 411 and the
detented end 405, 406 of connector 404. The connector 404
is assembled with metering plate 400 by inserting the
conical portion 407 into tapered opening 401. When the tube
connector is assembled with the metering plate, the spring
fingers 405, 406 engage fuel cavity 402, the beads 408, 409
provide a fluid tight seal with opening 401 and raised ;~
portions 410 engage depressions 403 such that tube connector :
404 is fixed in a desired orientation with respect to metering
plate 400.
A further modified form of throat member 420 is
shown to enlarged scale in FIGURES 33, 34 and 35. Referring
to FIGURE 33, throat member includes an internal cylindrical
portion 421 joining a frusto-conical portion 422 which in
turn joins a restricted band 423 defining a venturi, located
between the mixture outlet end 424 and the air inlet end
425. As shown in FIGURE 33, restricted b~nd 423 is disposed
eccentrically with respect to cylindrical portion 421. A
main fuel aperture 426 opens through a wall of restricted
band 423 providing communication with a fuel slot 427, and
an idle fuel aperture 428 opens into cylindrical portion 421
of the mixing passage providing communication with idle fuel
slot 429. The arrangement of conical portion 422 and eccentric
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restricted band 423 is effective to prevent the formation of
static pressure zones in the mixing passage. Fuel slots
427 and ~29 are provided with a pattern of raised beads 430,
431 extending aro~md the slots which are compressed to form
a fluid tight seal when the throat member is assembled with
a corresponding base plate, metering plate and cover plate.
A further modified feature of throat member 420 is that
lateral ears 432, 433 are provided instead of beveled keys.
Ears 432, 433 are of different lengths which provide an
alternate means for coding a throat member for use with a
corresponding metering plate and assuring that the fuel
apertures in a throat member are correctly oriented with
respect to a fuel module.
While it is believed that the operation of diaphragm
carburetors is well understood by those skilled in the art,
a brief explanaton of the operation of the present carburetor
will be given referring initially to FIGURES 5 and 6. The
idle fuel channel means is shown in FIGURE 5 in combination
with a common portion of the fuel channel, while the main or
high speed portion of the fuel channel is shown in FIGURE 6
in combination with a common portion of the fuel channel.
Referring now to FIGURES 5, and 6 the tube connector
200 is connected to a source of fuel such as a fuel tank not
shown in the drawings. Fuel is normally present in fuel
cavity 201. Alternating pressure pulses are applied to a
portion of diaphragm 59 through opening ll9, such alternating
pressure pulses being available from the crankcase of a
reciprocating engine with which the carburetor is used. The
application of such alternating pressure pulses to the
diaphragm causes fuel to be withdrawn from cavity 201
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through flap valve 253 into fuel pump recess 204 and then
expelled from the fuel pump recess 204 through flap valve
256 into recess 289, As fuel is withdrawn fro~ metering
chamber 207 through orifices 213 or 214, the diaphragm rises
causing valve 60 to open valve seat 208 which admits fuel to
thP metering chamber from recess 289. :~
When the throttle plate 115 is in closed, or idle, -~ :
position as shown in FIGURE 5, engine vacuum is imposed on
idle orifice 111 and on idle channel portions 122, 234, 2~0
and around metering plug 70, to idle metering orifice 213,
channel 281 and air bleed orifice 193. Engine vacuum is
effective to draw air through air bleed inle~ 127 and fuel
through idle metering orifice ~13 to create an air-fuel
emulsion in the pocket around metering plug 70. The air-
fuel emulsion is delivered to the mixing passage 107 through
channel portions 280, ~34, 12~ and idle orifice 111.
When the throttle pla~e 115 is in the closed
position as shown in FIGURE 5, the accelerator pump cam 104
is in the inactive position shown in FIGURE 8 which permits
pump recess 287 to fill with fuel. Sight glass 73 provides
a means of visual inspection to determine whether fuel is
present adjacent the throat member.
When the throttle is moved to open position as
shown in FIGURE 6, accelerator pump cam 104 pushes upwardly
on shoe 64 expelling fuel from cavity 287 through channel
portion 286, 285, 283, 282, 225, 226, 227 and 228 into slot
320 and through fuel apertures 110, 112 into the mixing
passage. Thereafter, the inducted air passing through
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restricted band 105 creates a vacuum condition in channel
portions 228, 227, 226, 225 and recess 220 which draws fuel
from metering chamber 207 through metering orifice 214. The
purpose of check ball 65 is to prevent back bleeding of air
through the high speed ~uel channels when the carburetor is
operated at idle condition.
Among the advantages of the present carburetor
construction are that the fuel channels are formed as simple
recesses and openings which avoids the drilling of complex
intersecting passages. Another advantage is that components
of the carburetor are designed for nested assembly with
other components which facilitates assembly, avoids machine
finishing to close tolerances and results in a compact
assembly. ~ still further advantage of the carburetor is
that certain components are formed for interlocking assembly
with adjacent components which reduces the numbers of screw
fasteners required, and provides a means of correctly
orienting one component with respect to another during
assembly. In addition, interlocking means can be provided
in a form to facilitate the selection and assembly of a
desired combination o~ interchangeable components. Many of
the components can be formed of metal or synthetic resinous
materials by simple molding processes.
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